1. Field of the Invention
This invention relates to a method of diagnosing renal diseases, more specifically to a method of diagnosing renal diseases by detecting albumin fragments in human urinary sample.
2. Prior Art
Clinical diagnosis of nephropathy, particularly diagnosis of diabetic nephropathy has conventionally been carried out by monitoring patient's conditions such as continuous proteinuria, renal dysfunction and hypertension, because renal biopsy is difficult. However, it is difficult to cure nephropathy of a patient discharging proteinuria, and such nephropathy generally develops into terminal renal insufficiency within 5 or 6 years. Therefore, in the field of the clinical medicine, it has been strongly desired to diagnose renal diseases and cure the diseases before they are found by the positive results of proteinuria test by conventional proteinuria test paper methods.
The determination method of urinary microalbumin has been developed as a diagnosing method of renal diseases for this purpose, and this method has recently become indispensable test method to the diagnosis of nephropathy. Accurate quantitative determination of urinary microalbumin may be carried out by, for instance, RIA (radioimmunoassay) and immunoprecipitation. Simple test kits for this determination are also commercially available and there can be used "ALBUSURE" (Eisai Co., Ltd.) as an example of those kits. The assay system of this commercially available kit is based on the agglutination inhibition technique, and the kit contains albumin-immunized latex and anti-albumin antibodies as test reagents. In the assay using this kit, the latex is agglutinated by the antigen-antibody reaction when albumin is substantially absent in the urinary sample whereas the latex is not agglutinated when the urinary sample contains albumin, which inhibits the antigen-antibody reaction.
As described above, methods of diagnosing renal diseases by determination of urinary microalbumin have been already known. However, urinary microalbumin of a patient indicates that the patient is in an early stage of nephropathy, which corresponds to the period of 6 to 20 years from the crisis of diabetes, and the nephropathy in such a stage is likely to develop into the forth stage of nephropathy (manifest nephropathy). (The stages of nephropathy are represented according to the classification of Mogensen, N. Engl. J. Med., 310, 356, 1984.)
Therefore, there still remains a need to develop a method of diagnosing nephropathy, which enables the diagnosis of nephropathy in an earlier stage thereof.